The new ASTM R-values for sleeping mats

By Sea to Summit

#GUIDE #SLEEPINGMAT #TESTING

In the case of the new ASTM R-values, change is a very good thing. And we’ve compiled some Frequently Asked Questions so you can brush up on this new industry standard for sleeping mat testing.

What’s an R-value?

An R-value (Resistance-value) is a metric used to rate how effectively your sleeping mat resists heat loss. It’s the only way to know how well your mat will prevent your body heat being leeched away by ground temperatures (which can be a lot colder than air temperatures).

This value can be tested in-house but at Sea to Summit our mats are independently tested at a laboratory to precisely controlled standards.

Are R-values changing?

The R-value metric remains the same, it’s the testing for this value that has been updated.

The new industry standard ASTM F3340-18 testing has now been introduced and all Sea to Summit mats released from 2020 onwards will be tested to this standard.

While we’ve always had our mats independently tested for R-value, many brands will now start publishing R-values for the first time, which will make it much easier to compare ASTM F3340-18 tested mats across different brands.

Standardising R-values, much like the EN rating on sleeping bags, will take a lot of the insecurity out of purchasing one of the most important items in your sleep system. It’s great news for you and our industry as a whole.

If you’ve always tested for R-values, why have some of your R-values changed?

To encourage publishing R-values across the board, Sea to Summit and other industry leaders formed a working group to ensure R-value testing is completely consistent across different brands.

The resulting methodology has been tweaked to achieve consistency in results—taking into account factors like mat pressure, ambient temperature and direction of heat flow.

If the R-value on my mat is lower or higher now, does that mean it’s colder or warmer than previously thought?

Nope, it just means that’s where it sits now on a universal scale—so you can compare sleeping mats between brands.

The new ASTM standard utilises a different testing procedure to previous tests. While this has produced some varied R-values for Sea to Summit mats—some a little higher, some a bit lower—it does not mean any of our mats are now warmer or colder.

Your old mat will perform in the same way as the same model tested to the new ASTM standard—even if the R-value published may be different.

Can you give me a comparable temperature range for each R-value?

If only. It’s not an exact science—every person sleeps differently.

When it comes to heat loss in sleeping mats, you’re not just accounting for the air temperature but, more importantly, the ground temperature—which can be a lot colder than the air (or in some instances, warmer!). After all, it is the ground that your sleeping mat is insulating you from.

Ground temperature measurements rarely get a mention in any weather report. Combine this with factors like gender (women tend to sleep a few degrees colder than men), caloric intake, shelter and sleeping bag choice, the whole temperature game suddenly gets pretty complicated.

Temperature and seasonal guides are riddled with variables, but we know many people rely on these to make purchasing decisions—so we’ve provided rough temperature ranges and seasonal guides to give you an idea of which R-value is best suited to your use.

Any temperature or seasonality guides (from all brands) need to be taken for what they are—a rough guide to further assist you.

Consider Sea to Summit’s Head Office location in Perth, Western Australia. Here, overnight lows in winter are around 12 degrees Celsius (60 Fahrenheit!), though the wind can make it feel many degrees colder. This is what our winter feels like, but yours may feel very different.

Which R-value do I need for which season?

Seasons are different everywhere—here in South West of Australia, we actually have six seasons—but most people around the world have a pretty good gauge of what warm, cool, cold and extreme weather feel like.

Choose a higher R-value if:

Use the above R-value guide to choose the best match for your sleeping conditions and then consider the below factors. If any of these apply to you, compensate by choosing a higher R-value (the higher the R-value, the more suitable it is for colder temperatures). If more than one of these apply to you, consider choosing a mat made for colder conditions.

  • You know the ground temperatures are much lower than the air temperatures
  • You are a woman (most women sleep a few degrees colder)
  • You are a cold sleeper
  • There is a lot of cold wind where you camp

Will a high R-value mat be too hot for summer?

Yes and no. Mats with higher R-values tend to insulate in a few ways. We use Exkin® Platinum in our air mats to create a reflective barrier that prevents heat loss by radiation and an insulating material like THERMOLITE® to slow air movement and reduce heat loss by convection.

Our higher R-value mats may not allow you to cool down as efficiently as a mat with a lower R-value (if the ground is cooler than the air). This also works in reverse—if the ground temperature is warmer than the air temperature, you’ll stay cooler with a higher R-value sleeping mat.

Is it safer to choose a higher or lower R-value for your purpose?

Temperature-wise, a mat with a higher R-value will always have more versatility of use than a mat with a lower R-value. It all depends how much weight you’re willing to carry around to ensure you’ve covered your bases. Some people want just the right amount (so they don’t carry any more grams than necessary), some are happy to go a little bit under (and boost warmth with a thermal liner or warmer bag when needed) and some would rather choose a mat with a higher R-value just to be safe.

Does my mat have the new R-value or the old R-value?

Any mat that has been tested using the new ASTM standard will be labelled accordingly on its packaging. On the product itself, there will be a sticker. You can also check the model against our website for the updated ASTM standard R-value (if it changes at all) from 1 Jan 2020.

How are the ASTM R-values tested?

R-values (resistance to heat flow) are measured by placing a hot plate on one side of a sleeping mat and a cold plate on the other. Electronic sensors then determine how much energy it takes to keep the hot plate at a consistent body heat.

Now, here’s some real gear nerd stuff…

During this test, the sleeping mat must be inflated to a specific pressure (0.5 psi) and the hot plate must be applied to at 2pa pressure. The temperature of the heated plate is set at 35֯C / 95֯F to mimic body heat. Don’t even get us started on how to calibrate the machine first, we’ll be here all day.

How was the old R-value calculated/tested?

At Sea to Summit, we’ve been testing our R-values in a very similar way to how it’s tested now. However, the methodology has been tweaked to be consistent across other brands.

Who is adopting this new standard?

Most of the well-known brands like Sea to Summit will be using this new standard. Hopefully, everyone will jump on the bandwagon. It’s a very good bandwagon that makes comparison easier for you.

Is this a legal standard?

No. Not all sleeping mats need to be tested using this standard and, therefore, many sleeping mats will continue to publish R-values according to their own metrics. Which makes apples-to-apples comparison more difficult between brands.

However, only sleeping mats tested using the new standard can use the ‘ASTM’ markings. When looking for your new sleeping mat, and comparing R-values, ensure you compare mats that are being tested to the new standard.

Most well-known brands will be using this new standard.

What if you purchase a mat with an R-value that isn’t warm enough?

If you purchase a mat that isn’t quite warm enough out in the wild, there are a number of ways you can boost the temperature. You can get a warmer sleeping bag, add a thermal liner or even add another sleeping mat. R-values are additive so if you pair a mat with an R-value of 2 with an R-value of 3, you’ll get a combined R-value of 5. You could also add clothing layers, boost your caloric intake or do some push ups before getting into your sleep system.

What should you consider when purchasing a sleeping mat first and foremost?

There are so many sleeping mat options on the market, trying to decide on one can make your brain hurt. There are many things to consider when trying to narrow down which mat to choose, including:

  • Comfort
  • ASTM F3340-18 R-value
  • Construction
  • Weight + size
  • Packability
  • Method of inflation

To make life easier, we’ve narrowed it down to the three most important things to consider when choosing a sleeping mat.

How do you know what R-value you need?

The higher the R-value number, the more insulating it will be. If you hike in mostly warm climates you would choose a mat with a lower R-value (0–2 maybe). If you are hiking in winter or cold climates that reach 0 degrees or below, choose a mat that has a higher R-value (4–6).

Then consider other factors that might make you warmer or colder at night and move up and down the R-value scale accordingly.

Of course, you can also just skip the lessons in insulation and thermodynamics and head straight to our Sleep System Finder, which will do the work for you.

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